Single photon-emission computed tomography (SPECT) is a well-established procedure in diagnostic nuclear medicine used for a variety of studies, of which cardiac and brain imaging are the most important. The nuclear medicine used for a variety of studies, of which cardiac and brain imaging are the most important. The tomographic image quality, which ultimately determines the diagnostic utility of SPECT, depends mainly on the number of photons that can be collected during a patient scan. This proposal describes an inexpensive, novel adaptation of SPECT that will provide at two to four times the photon sensitivity, thereby allowing significantly improved detection of lesions or increased patient throughput due to shorter scan times. The conventional parallel-hole collimator is replaced by a rotating slant- hole (RSH) collimator whose multiple segments simultaneously gather two or more projection views of the organ of interest. This increased photon sensitivity comes at the cost of a reduced active imaging region (the "common volume" or CV in the proposal), so the approach is useful only for imaging smaller organs such as the heart and brain. Converging collimators, such as fan-beam, cone-beam, and variable focal-length collimators, apply athe same principle of reducing the CV to gain sensitivity, but rarely achieve even a factor of two increase in sensitivity, and most of them introduce image reconstruction difficulties and require extended scanning motions for a tomographically complete dataset. The RSH SPECT geometry requires no extra scanning motions and uses straightforward three-dimensional (3D) image reconstruction techniques. The goal of this project is to build and evaluate a prototype RSH SPECT scanner. The primary objective is to demonstrate increased photon sensitivity. Other major issues are; susceptibility to background activity: correction procedures for photon attenuation; and patient positioning with a limited imaging volume. The unique combination of collimator rotation with detector gantry motion introduces some unexpected and interesting features. The fully 3D geometry introduces new challenges for attenuation correction methods. An unusual sensitive region (SV) to background radioactivity suggests an attractive new scanning configuration for brain imaging, but might introduce artifacts in heart imaging if there is strong uptake in nearby organs. The research program consists of 5 stages. Stage I involves collimator design and software development. Stage II consists of initial evaluations of the prototype scanner using phantoms. Stage II addresses the problem of attenuation correction for this unusual tomographic geometry; several approaches will be implemented and evaluated. In stage IV, state-of-the- art corrections for Compton scattered background and geometric collimator response will be implemented. In stage V a set of phantom experiments will be used to evaluate and characterize the RSH SPECT system. The main experimental tools, computer stimulations and phantoms, will be developed at the beginning of the project.